<template>
  <div>
    <ul class="list">
      <li class="item" v-for="item in letters" :key="item" :ref="item"
      @touchstart="handleTouchStart" 
      @touchmove="handleTouchMove" 
      @touchend="handleTouchEnd" 
      @click="handleLetterClick">{{item}}</li>
    </ul>
  </div>
</template>

<script>
export default {
  name:'CityAlphabet',
  data(){
    return{
      touchStatus:false,
      startY:0,
      timer:null
    }
  },
  props:{
    cities :Object
  },
  updated(){
    this.startY = this.$refs['A'][0].offsetTop;
  },
  computed:{
    letters(){
      let letters = [];
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters;
      console.log(letters);
      
    }
  },
  methods:{
    handleLetterClick(e){
      // console.log(e.target.innerText);
      this.$emit('Change',e.target.innerText)
    },
    handleTouchStart(){
      this.touchStatus = true;
    },
    handleTouchMove(e){
      if (this.touchStatus) {
        if (this.timer) {
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(() => {
          const touchY = e.touches[0].clientY-79
          // console.log(touchY);
          const index = Math.floor((touchY-this.startY) / 20)
          console.log(index);
          if (index>=0 && index<= this.letters.length) {
            this.$emit('Change',this.letters[index])  
          }  
        }, 16);  
      }
    },
    handleTouchEnd(){
      this.touchStatus = false;      
    }
  }
}
</script>

<style lang="stylus" scoped>
@import '~@/assets/styles/varibles.styl'
  .list
    display :flex
    flex-direction :column
    justify-content :center 
    position absolute
    top :1.58rem
    right :0
    bottom :0
    width :.4rem
    .item
      line-height :.4rem
      text-align :center
      color :$bgColoer
</style>
